1. Field of the Disclosure
This disclosure generally relates to an optical touch system and, more particularly, to an exposure mechanism of an optical touch system and an optical touch system using the same that may shorten a total retrieval time of a bright image and a dark image spent by all image sensors.
2. Description of Related Art
An optical touch system generally utilizes a plurality of image sensors to sequentially capture a plurality of image frames containing a touch surface image and performs the object tracking according to the position of a finger image in the image frames.
For example referring to FIG. 1A, it shows a schematic diagram of the conventional optical touch system 9, which includes a touch surface 91, four image sensors 921-924 and four active light sources 931-934. When each of the image sensors 921-924 is capturing an image frame, the associated active light sources 931-934 irradiate so as to provide light for capturing the image frame.
Conventionally, it is able to calculate a differential image between a bright image and a dark image so as to eliminate the interference from ambient light.
For example referring to FIG. 1B, the image sensor 921 captures a bright image ION corresponding to the irradiation of the active light source 931 and then captures a dark image IOFF corresponding to the extinction of the active light source 931. And the image sensors 922 to 924 operate similarly. A processing unit (not shown) is configured to calculate a differential image (ION−IOFF) between the bright image ION and the dark image IOFF, and to perform the object positioning according to the differential image. It is assumed that a sampling interval of the image sensors 921 to 924 is T such that a total retrieval time for capturing a bright image ION and a dark image IOFF by all the image sensors 921-924 equals 8T. In this manner, the synchronization between the image sensors 921-924 for capturing image frames is decreased. Especially when the number of the image sensors is increased, the total retrieval time for capturing a bright image and a dark image by all the image sensors becomes longer.
Accordingly, the present disclosure further provides an exposure mechanism of an optical touch system and an optical touch system using the same that may shorten the total retrieval time of a sampling cycle thereby improving the synchronization between image sensors for capturing image frames and increasing the positioning accuracy.